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Jfet BOZ
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Old 20th January 2018, 11:15 AM   #1411
indra1 is offline indra1  Indonesia
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Andrew, he wants help with JBOZ driving single pair F4 output stage. Off course my rough guide is not complete. Please suggest more appropriate method as you see fit for a newbee.
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Old 20th January 2018, 01:56 PM   #1412
Vix is offline Vix  Yugoslavia
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I am currently using jfet Boz with J310. 24v supply, 680 ohm drain resistor, 220 source degeneration resistor. 100 ohm at the output. Works lovely. See schematic here:
Jfet BOZ
Post nr. 745
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Old 24th January 2018, 02:07 PM   #1413
marconi118 is offline marconi118  Germany
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Sorry for being rude in my previous posts, it was not intentional, only driven by ignorance. I need to learn...

I choose the JBOZ because it is the simplest schema useful for new-by.

what jfet should I use to achieve the low output Z and good sound?
BF862, BF861A,B,C J309 J310
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Old 24th January 2018, 02:34 PM   #1414
indra1 is offline indra1  Indonesia
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Quote:
Originally Posted by marconi118 View Post
....I choose the JBOZ because it is the simplest schema useful for new-by....
I believe working with Mosfet is easier for a beginner, almost plug and play while matching and biasing is unavoidable for the jfets. But it is your project, go with your choice.

All the jfets you mentioned will give you output impedance low enough for F4 and nice sound when biased correctly. However, each will have different sound signature. You will need to ask a very gifted oracle to tell you which will sound the best to you before a build.

I like the 2SK147 in my system, but others will say they prefer the J310 in their system and your system will most likely be different. Are you willing to match my system and listening room and try the 2SK147? What if you prefer the J310 even if you match my system? Would you be content if I tell you to use the 2SK147 because it is the goddamn best I have ever heard? What if your taste and mine are different?
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Old 24th January 2018, 03:04 PM   #1415
marconi118 is offline marconi118  Germany
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the only thing that I don't understand fully is about the low output Z.
for low Z you need a low value of drain resistor, therefore high Id. in this case the J310 and BF861C should be more suited?
2SK147 is hard to get?
nothing against mosfets indeed, and easy bias via pot on the gate.
I could try it with irf610 la moosefet
or use BS170 or BS270 like JUMA did? any advice on the sound?
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Old 24th January 2018, 04:39 PM   #1416
indra1 is offline indra1  Indonesia
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Bias and impedance are requirement for the circuit to get sufficient output without letting the magic smoke out. The sound however is another matter, they are all different, and I regretfully only try very few of them in preamp duty before settling with DHT.

2SK147 is harder to get compared to the 2SK170. Be prepared to get fakes. Mouser stock Interfet substitute IFN147 which sell for $7.65.

In a Moosefet, the IRF610 is a bit more polite while the IRF510 has more slam and zing. My business partner once compared a ECC88 tube preamp and a BS170 preamp ala BOZ a customer brought in and can not pick which sounds better to him.
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Old 25th January 2018, 10:32 AM   #1417
marconi118 is offline marconi118  Germany
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with BS170 will it be more tubish than IRB610 or 2sk147?
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Old 25th January 2018, 11:32 AM   #1418
indra1 is offline indra1  Indonesia
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I have not heard the BS170 myself. I think if you want really strong tubish you would prefer the rare small signal Sony SIT jfet like 2SK79 or 2SK63. Go ahead and obtain some before they become unobtainium, liubincalvin sell matched pairs for $34. But I strongly suggest learning to build and tweak with more available jfets first to reduce the chance of wasting extremely rare parts on beginner's mistakes. Build separate good shunt regulated PSU for each channel with quiet soft recovery rectifiers to LC filtered raw supply.

Once you think you are ready for the SITs, I think you would understand your preferences a little better. I suggest loaded tube circuit style with transformer or choke (but nice finemet ones start north of $200 each), or at least gyrators like Ale Moglia's Gyrator Boards (calls for good quality caps like teflon or polystyrene). Most of us start with what our budget allows and save for the upgrades.
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Old 25th January 2018, 02:06 PM   #1419
marconi118 is offline marconi118  Germany
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I will start with bs170. Buy sits and spare for the future

Was the bs170 boz resistor or ccs or gyrator loaded? Juma published a nice gyrator loaded cascoded jboz
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Old 25th January 2018, 02:20 PM   #1420
indra1 is offline indra1  Indonesia
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I'm quite sure it was resistor loaded, but properly executed gyrator loaded will be superior in dynamics due to lower output impedance.
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